Can you add a class match with omshell?

[Peter Grandi]

Hi, I have a classic question, which is that I have a Nortel
5500 router with 3 interfaces and with DHCP relay configured on
it, forwarding to a 3.0.x (I think) 'dhcpd'.

The router receives the DHCP broadcast on one subnet but the
source address of the DHCP unicast into which it is translated
is on another (the one for the route to the DHCP server).

The 3 interfaces are: 172.23.98.254/24 (forwarder), and
172.23.66.98/24, 172.23.68.98/24, and 'dhcpd' seems to match the
subnet on the source address of the packet (172.23.68.98)
instead of the gateway address ('GIADDR') inside the packet
(172.23.98.254).

I have done some searching for postings and looked at the
sources ('dhpc.c' 'locate_network()' for example) and it is not
clear how to work around.

Some  said that this happens when 'shared-network {}' is
used, for example, and some other seem to say that the source IP
address is always used; the sources seem to prefer the 'GIADDR':

       /* If there's no SSO and no giaddr, then use the shared_network
           from the interface, if there is one.   If not, fail. */
        if (!oc && !packet -> raw -> giaddr.s_addr) {
                if (packet -> interface -> shared_network) {

So I am perplexed. What should I be looking for or checking?